Pretreatment of cellulosic textiles with melamine formaldehyde resin



Patented July 1, 1947 PRETREATMEN T OF CELLULOSIC TEXTILES WITH MELAMINEFQRMALDEHYDE RESIN John D. Pollard, Stamford, Conn, assignor to AmericanCyanamid Company, New York, N. Y., a corporation of Maine 9 No Drawing.Application December 30, 1943,

Serial No. 516,249

This invention relates to the bonding of textile filaments, fibers,threads, cords and fabrics composed of or comprising hydroxyl-containingcellulosic material to coatings, and more particularly to thepretreatment of such cellulosic textiles to form an anchorage forcoatings that may subsequently be applied. The invention includes thepretreated cellulosic textiles themselves, methods of pretreatmentwhereby the bonding properties of the cellulose or cellulosic textilesare improved, and coated cellulosic textiles wherein a stronger and morepermanent bond is obtained between the cellulosic base material and theapplied coatmg.

An extremely wide variety of coating, laminating or impregnatingmaterials have heretofore been applied to cellulosic threads, fibers,fabrics and the like.. Thus, for example, a wide variety ofwaterproofing materials have been coated upon cotton, rayon and similarfabrics in the production of raincoats, water-proof bags and the like,including such materials as natural or synthetic rubber, cyclizedrubber, chlorinated rubber, polyvinyl butyral coatings includingmixtures of polyvinyl butyral with alkyd resins, as well as syntheticresin compositions and the like. Similarly linoxyn coatings, with orWithout the addition of ground cork, zinc oxide and other fillers havebeen applied to cellulosic backings in the preparation of oilcloth,certain types of linoleum and the like. The present invention in itsbroader aspects is not limited to coated compositions con taining anyone or more coating materials, but is directed primarily to a method ofpretreating the cellulosic material in such a manner as to improve itsbonding characteristics when coating materials are applied thereto.

I have found that the bonding properties of cellulosic textiles such asfilaments, threads, fibers, fabrics and the like are improved by theapplication thereto of an acidified aqueous colloidal solution ofpartially polymerized melamine-iormaldehyde resin. Although my inventionis not limited by any theory of operation. I believe that thisremarkable improvement is due to a modification of the surfacecharacteristics of the cellulosic textile fibers by the colloidalmelamine-formaldehyde resin. This opinion is supported by the fact thateven minute quantities of colloidal, water-insoluble resin on the orderof 0.01 of the 7 Claims. (Cl. 117-161) dry weight of the cellulosictextiles will produce a great increase in the bonding propertiesthereof, whereas a similar improvement is not obtained by impregnatingthe textiles with small or even moderately large amounts of the sameresin in an unpolymerized and water-soluble condition. My invention inits broader aspects therefore comprises the step of impregnatingcellulosic textiles with acidified aqueous colloidalmelamine-formaldehyde resin solution under conditions such that thetreated textile fibers contain small quantitles on the order of 0.01-2%of .the resin in a water-insoluble condition; i. e., in such a form thatthe colloidal resin is not removed by washing the fibers with waterimmediately after impregnation.

The aqueous colloidal solutions of partially polymerized melamineformaldehyde resin which are used in practicing my invention may be wepared by any one of several difiereni; procedures. Amelamine-formaldehyde condensation product may be dissolved in acidifiedwater which preferably contains sufiicient acid to produce a glasselectrode pH value within the range of about 0.5-4.0 when measured at12% resin solids content and the solution may then be aged at roomtemperature or at elevated temperatures until a hydrophilic colloid isformed. If desired, the aqueous solvent in which the resin is aged maycontain substantial quantities of a polyhydric alcohol such as glycerol,ethylene glycol and the like, but in this case it is not necessary touse such large quantities of acid and the desired hydrophilic colloidcan be obtained at pH values as high as 6.8,which means that thequantity of free acid in the solution is almost vanishingly small.However, the resin solution must always contain some water (usually atleast 20% for best results) and it must always be acidified with atleast a minute quantity of acid, as otherwise the desired hydrophiliccolloid is not obtained.

Substantial quantities of acid are extremely undesirable in cellulosictextiles, since they cause tendering and other forms of degradation ofthe cellulose. It is therefore a very important advantage of myinvention that the necessary quantities of the colloidalmelamine-formaldehyde resin are retained by the textile fibers in awaterinsoluble condition, for the fibers can be. washed with waterimmediately after they have been im- In cases where it is not feasibleto wash the textiles with water immediately after impregna-' tion thealcoholic solutions of melamine-formaldehyde resin may be used. Whenthese solutions contain about 20-90% of a polyhydric alcohol substance,the remainder being water and acid, the dissolved resin can be aged tothe colloidal condition with very weak acids such as acetic acid, andeven such weak acids need be used in only very small quantities. Thepresence of weak acids in the impregnated textiles in small quantitiesis not objectionable, and therefore it is easy to deposit the requisitesmall quantities of the colloidal resin on the textiles in awater-insoluble condition without damaging the fibers.

It has previously been proposed to apply melamine-formaldehyde resins totextile fabrics, including cotton and rayon fabrics, in such quantitlesas to render them creaseproof or to function as adhesives for stiffeningagents, filling agents, softening agents, water-repellents and the like.In all such cases, however, the melamine resin has been employed as aphysical bonding agent, and therefore amounts on the order of haveusually been impregnated into the fabrics. In such processes it is, ofcourse, impossible to wash the fabric immediately after theimpregnation, as the adhesive qualities of the resin are developed onlyafter it has been cured, and therefore the acid employed as a solvent orcuring agent is retained in the textiles. The present invention is basedon the discovery that small quantities of colloidal partiallypolymerized melamine-formaldehyde resin on the order of 0.0l-2% of theweight of the cellulosic textiles will impart greatly increased bondingproperties to the fibers thereof and on the further important discoverythat these quantities are retained by the fibers in a water-insolublecondition resistant to washing when the textiles are impregnated withthe acidified colloidal aqueous solutions. It is apparent, therefore,that the present invention accomplishes objects'which could not beattained by the processes of the prior art and is based on entirelydifferent principles. The invention in its broader aspects is notlimited by the type of cellulosic textile materials to which thecolloidal melamine-formaldehyde resins are applied, and improved bondingproperties are imparted to any such cellulosic textiles. Such materialsas regenerated cellulose including particularly viscose rayon,deacetylated cellulose acetate, denitrated cellulose nitrate, partiallymethylated, ethylated or otherwise etherified cellulose filaments, andthreads and fabrics composed of or containing partially esterifiedcellulose may be pretreated in accordance with the principles of theinvention. The resulting pretreated textiles may be coated with anysuitable coating, laminating or impregnating materials such as thoseenumerated above or other similar materials such as cellulosic coatings.

Although the bonding'properties of any cellulosic textile can beimproved by applying colloidal melamine-formaldehyde resin solutionsthereto there is a considerable difference in the retention of the resinby cellulose of various types. This difference appears to result fromdifferences in the degree of orientation or crystallization in thedifferent materials; thus, for example, in highly oriented cellulosefilaments such as are found in spun rayon the resin retention is muchlower than in comparatively unoriented fibers such as cotton fibers.Other forms of cellulosic textile materials may vary between these twoextremes. I have found, as a further important feature of my invention,that these differences in retention due to differences in orientationmay be compensated by proper adjustment of the age and particle size ofpartially polymerized melamineformaldehyde resin particles in thecolloidal treating solutions. These factors may be regulated byadjusting the acidity, solids content,

- temperature and aging time of the resin solutions prior to theirapplication to the textiles so that the best results can be obtainedwith each form of cellulose. Further adjustments may be made by varyingthe type of acid used to acidify the solution; thus, for example, whencellulose of low hydroxyl content is treated, such as cellulose acetaterayon, it is sometimes advantageous to add chloracetic oralpha-chlorpropionic acid to the originally clear melamine-formaldehyderesin solution either as the sole acidifying agent or in admixture withhydrochloric acid or other acids.

Similar variations in the acidity, solids content, age and particle sizeof the colloidal melamineformaldehyde resin solutions may also beemployed in pretreating fabrics designed for the application ofdifferent coating compositions. Thus, for example, in the application ofcertain types of polyvinyl acetal to rayon fabrics I have obtainedconsiderable improvements in the strength of the bond by employingchloracetic and hydrochloric acid mixtures as acidifying agents, Othervariations within the scope of the appended claims will readily suggestthemselves to those skilled in the art, and need not be furtherdetailed.

As is noted above, the presence of free acid in a cellulosic materialusually results in an undesirable degradation and loss in strength, andfor this reason it is very important to leave as little free acid aspossible on the fibers. In practicing the present invention this may bedone either by washing the textiles with water after the initialapplication of the resin solution, or by employing aqueous solutionscontaining polyhydric alcohols such as glycerine, ethylene glycol andthe like containing very small quantities of acid, or both. In thelatter case the subsequent washing step is of course not precluded, butthe washing does not have to be as thorough as when larger quantities ofacid are employed.

In view of the importance of avoiding the presence of substantialquantities of free acid on the textile fibers the resin retentionobtained with the colloidal, salt-sensitive melamine-formaldehyde resinsolution is an extremely important feature of the invention. Althoughthe quantity of resin that is retained after thorough washing of thetreated fibers with water will vary with the orientation orcrystallization of the cellulose, no difiiculty is encountered inobtaining retention of the extremely small quantities of the colloidalresin on the order of 0.0l-2% of the dry weight of the textiles that aresufficient to produce a stronger bond with coating materials. Largerquantities of applied resin are unnecessary and are usually undesirablesince they merely stiffen the textiles without further improving theirbonding properties.

Ordinarily the aged colloidal melamine-formaldehyde resin solutions areapplied to the cellulosic textiles at high dilutions on the order of0.1- 3%, although concentrations up to 6% and higher have been employedwith success. The more dilute solutions are usually preferred forseveral reasons; first, because of greater economy in the use of resin,secondly, because less acid is taken up by the textiles from more dilutesolutions, and finally, because of the greater ease of washing theimpregnated textiles. The resin solution may also contain plasticizers,softeners, finishing agents or other compatible ingredients for thetextiles, such as polyvinyl alcohol, polyethylene oxide having amolecular weight of 1500-4000, and the like.

In some cases even stronger bonding. is obtainable by pretreating thecellulosic material prior to the application of the resin colloidthereto. Thus, for example, regenerated cellulose filaments can bepretreated with alcoholic sodium hydroxide and then with alcoholicchloracetic acid or with an alkaline sodium chloracetate solution' inalcohol. When samples of finished rayon cloth were pretreated in thismanner and then impregnated with a 3% aqueous solution ofmelamine-formaldehyde resin that had been acidified with 0.8 molof HClper mol of melamine and aged -18 hours the bonding properties of thefabric to a commercial alkyd-butyral coating composition were greatlyincreased.

After impregnating the textiles with the colloidal aqueousmelamine-formaldehyde resin solution followed by washing if desired anddrying, the textiles are usually treated to cure the applied resin.However this curing step is greatly facilitated by the partially.polymerized condition in which the resin is applied to the fibers, foronly a small amount of additional treatment is necessary to complete thecure of the resin. Thus I have found that the resin will curespontaneously upon storage of the treated fibers at temperatures as lowas 70 F., although ordinarily higher temperatures up to about 240 F. arepreferred because of the greater curing speed. It is evident, therefore,that no special curing equipment is necessary in practicing the presentinvention; ordinary steam or hot air driers may be employed and thecuring of the resin may be accomplished at the same temperatures andunder the conditions that are usually employed to dry the textilefibers.

The invention will be illustrated in greater detail by the followingspecific examples. It should be understood, however, that although theseexamples may describe in detail some of the more specific features ofthe invention, they are given primarily for purposes of illustration andthe invention in its broader aspects is not limited thereto.

EXAMPLE 1 Melamine-formaldehyde resin solutions were prepared fromsubstantially monomeric methylol melamine obtained by the followingprocedure:

Melamine was added to substantially neutral 37% aqueous formaldehydesolution in the molecular ratio of 1 mol of melamine for each 3.3 molsof formaldehyde and the solution was heated at 60 C. for thirty minutes.The resulting syrup was cooled to separate out crystals of methylolmelamine which were centrifuged and dried.

Water solutions containing 12% of the methylol melamine were preparedand acidified by the addition of 1.2 mols of concentrated hydrochloricacid for each mol of melamine. In order to determine the effect of agingthe solution, samples of unsized viscose rayon fabrics were impregnatedin the unaged solution at 3% solids and after dilution with water to0.5% resin solids. Other solutions were aged at ro m t p ra ur s fordefinite periods of time and then diluted and used to impregnate othersamples of the same rayon fabric. All the rayon fabrics were washedthoroughly in warm water to remove the acid and mechanically held resinand were then heated for ten minutes at 200 C.

The pretreated fabrics were then laminated at 70 C. and 120 pounds persquare inch pressure to an uncured polyvinyl butyral coated cottonfabric of commercial grade and the laminated fabrics were cured withoutpressure in an oven for one hour at 250 F. The cured test pieces werethen evaluated for adhesion on a Schopper tensile testing machin by theprocedure described in Example 3 at a speed of 4 inches per minute. Theresults are given in the following table:

1 are 35 Age of 3% soln. before use vsvollil.1 i ifi g applied width 1 2minutes 0.5 1. 8-2. 2 2 2 minutes 3.0 2. 4 2. 8 3 3 hours.- 0.5 1 3hours..- 3.0 1 6 hours..- 0.5 l 6 hours... 3.0 l 24 hours.. 0.5 1 24hours 3.0 1 Control, washed and dried None 1.8-2 4 1 The cotton backingwas pulled from the sample.

The importance of aging the acidified solutions is clear from the aboveresults. Only a very slight improvement in the bond between the rayonand th coating was obtained when a monomeric resin was used, but whenthe resin .h'ad been partially polymerized to the colloidal condition byaging the acidified solutions the strength of the bond was greatlyincreased.

EXAMPLE 2 A partially polymerized melamine-formaldehyde resin wasprepared as follows:

To 115 pounds of a commercial 37% aqueous formalin was added 59.5 poundsof melamine and the pH of the resulting slurry was adjusted .to 7.0 bythe addition of sodium hydroxide solution. The slurry was then heated toC. and maintained at this temperature for 30 minutes, whereupon thebatch was cooled to 70 C. and held until it became hydrophobic as shownby the formation of a white cloud when a few drops were added to waterat 60 C. The pH was then adjusted to 9.0 and the batch was'cooled andsprayed into a current of hot gases (420 F.) in a commercial spraydryer. The finely divided,

spray-dried product was obtained as a white, wa- I ter-insoluble powder.

An acidified 12% solution was prepared by discotton fabric and testedfor adhesion strength as described in Example 3. The following resultswere obtained:

l The cotton backing was pulled from the sample.

These results, when compared with those of Example 1, show that thenecessary polymerization of the melamine-formaldehyde resin can beobtained either during the manufacture of the resin, or by aging anacidified solution of the resin, orboth. In all cases, however, theresin must be in a partially polymerized condition, as otherwise thestrength of the bond is not improved by small amounts of the resin, andin all cases acid must be present to keep the partially polymerizedresin in solution and aid in its adsorption by the textile fibers.

EXAMPLE 3 Colloidal solutions of the resin described in Example 2 wereprepared by dissolving 25 gram portions in acidified water heated to130-140 F. followed by dilution with cold water to a total volume of 208cc., this being a resin solids content of 12%, and aging at roomtemperature for 24 hours, Samples of unsized viscose rayon fabrics werepadded in these solutions, washed with water, dried in a tentering framefor ten minutes at 200 F. and the dried fabrics were then laminated at70 C. and 120 pounds per square inch pressure to an uncured polyvinylbutyral coated cotton fabric of a commercial grade and cured withoutpressure in an oven for one hour at 250 F.

The cured test pieces were evaluated for adhesion on a Schopper tensiletesting machine, using 0.5 inch wide test strips and a speed of 4 inchesper minute, and the results were expressed as pounds per inch widthnecessary to pull the pieces apart. In this particular commercial fabricthe polyvinyl butyral coating pulled away from its cotton backing at atension of 5-6 pounds per inch width, and highervalues could not bemeasured. It was apparent, however, that all of the resin-pretreatedrayon samples had a much higher degree of coating adhesion since theyremained firmly bonded to the resin while the latter was stripped fromthe cotton.

Wet adhesion values were obtained by soaking the laminated pieces inwater at room temperature for 48 hours and then measuring the pullrequired to separate the strips.

Resin solutions prepared with varying amounts of different acids wereapplied. In all cases the fabric was washed thoroughly in water at roomtemperature to remove the acid and excess resin immediately afterimpregnation with the resin solution and before drying. In the followingtable the amount of acid is based on 1 mol of melamine; the treatingsolution contained 3% resin solids and the pH was measured at thisdilution. The percent resin is based on the dry weight of the fabric.

Agjheslllen, No. 5.]

Molar quantity of acid pH Dry Wet butyric.

0.6 HCl, 0.4 hydroxy isobutyric.

0.4 BC], 0.6 hydroxy isobutyric.

0.8 HCl, 0.2 phthalic 1 The cotton backing was pulled from the sample.

EXAMPLE 4 A water solution containing 12% of the resin described inExample 2 and 0.8 mol of HCl per mol of melamine in the resin was agedat room temperature until a blue colloidal haze formed in the solution.Rayon samples were then padded in the colloidal solution at varyingconcentrations, washed thoroughly, dried and laminated and tested, usingthe materials and test procedure described in Example 3 except that thewet adhesion was determined after soaking in water for 72 hours. Theresin retained by the fiber was determined by Kjeldahl nitrogenanalysis. The results obtained were as follows:

Per cent Resin Adhesion, 1bs./in.

Sample No. I O h d n nwas e soln. fabric Dry I The cotton backing waspulled from the sample.

These results show that a great increase in adhesion is obtained wheneven a small trace of the cationic resin is retained on the fiber.

EXAMPLE 5 Rayon test pieces were immersed in solutions prepared bydissolving the resin described in Example 2 to 12% solids in watercontaining 0.6 mol HCl per mol of melamine, aging two hours at roomtemperature and diluting to 3% solids. The impregnated pieces were thenwashed thoroughly in warm water and dried and cured at varyingtemperatures. Some of the pieces were then boiled for two minutes in amixture of ethyl acetate, 25% toluene and 10% ethyl alcohol, rinsed inethyl alcohol and dried for five minutes in an oven at 200 F. All of thepieces were then laminated to polyvinyl butyral-coated cotton and testedas in Example 2." The following results were obtained.

l The cotton backing was pulled away from the sample.

Th e fi res show that the bonding qualities imparted by the resin arenot dependent on the curing temperaturesused, since good results wereobtained at room temperatures and at temperatures of 240 F.

Eiauamffi Per cent Resin in Dry Adhe- Type Fabnc ic sion, lbs/in.

1.. Cotton poplin... Control, Noresin. 3.0 l d 0.16 -6 80 x 80 cotton.Control,No resin. 3.4-3. 8 .d0 0.3 5-6 l The original cotton backing waspulled away from the sample. EXAMPLE 7 Solution No. 11 mol HCl SolutionNo. 20.8 mol HCl; 0.2 mol chloracetic acid Solution No. 3-0.8 mol HCl;0.2 mol oc-ChlOI'DIO- picnic acid Rayon tire cords were pretreated inthese solutions to improve their bonding properties to rubber. Corduracords were impregnated with the resins, washed thoroughly in Water,dried and heated 15 minutes at 200 F. They were then heated underpressure with sections of uncured rubber, both natural and synthetic.The finished pieces, consisting of cords embedded in cured rub- -BUNA SRUBBER No treatment 1.3 l. 0 1.15 100 Water washed"... 1.4' 1.1 1.25 109Soln. No. l 0. 70 1. 9 1. 5 l. 70 148 $0111. No. 2 0.88 1.6 1.3 1. 126S0111. No. 3 0.78 1. 5 1. 2 1.35 117 EXAMPLE 8 man the precedingexamples fairly large quantitles of acid were used in water solution toform colloidal aqueous solutions of the melamine-formaldehyde resin andthe treated cloth waswashed to remove the acid, leaving small buteffective quantities of the resin adhering thereto. Numerous solventsother than water may be used as dispersing agents formelamine-formaldehyde resins, and I have found that the resin can beconverted to the colloidal condition with the aid of much smallerquantities of aqueous acid when water-soluble dior polyhydric alcoholsor their ethers are present. Typical solvents of this class which may beused are ethylene glycol, glycerol, diglycerol, polyethylene glycols andtheir monoethers such as the monoethyl ether of ethylene glycol as wellas glucose and sucrose. Monohydric alcohols have been tested, but failto give satisfactory colloidal solutions when reduced quantities ofaqueous acid are used.

Several factors govern the optimum proportions of polyhydric alcohols tobe used. At a given resin solids content, such as 12%, very concentratedaqueous solutions containing 80-95% of glycerol or ethylene glycol mustbe used to dissolve the resin when no aqueous acid is present. If,however, an aqueous acid solution is used in conjunction with thepolyhydric alcohol solvent.

the amount of alcohol can be reduced; thus with 0.1 mol of acetic acidper mol of resin only 60% of the alcohol need be used. As the pH isreduced the amount of alcohol necessary is also reduced; for example, if0.5 mol of acetic acid is used a 40% glycerine or ethylene glycolsolution will serveas a solvent.

The aging of acidified solutions containing a high concentration ofpolyhydric alcohol is very her, were evaluated by measuring the punslow; in fact, the colloidal condition is not quired to strip the cordsfrom the rubber. The reached m F mqnihs at f temperatures in testresults are shown in the following table: a 12% resm Solutlon contalmng95% glycerol 1 mol of H01 per mol of melamine and 5% Water. Adhesiontest results However, if the solution is diluted to contain at least 20%of water the aging period is reduced to Per cent Av of Av 0 Mean PercentPretreatment Resin m h-igh lbs. Adhesion 24 hours or less at this highacid concentration, tamed pulled and the same results are obtained withsomewhat NATURAL RUBBER longer aging times when greatly reducedquantities of acid are used. This is shown by the fol- No treatment 2. 1l. 5 1.80 100 Water washeiw m L 4 L 97 r lowing experimental results,which were obtained E0111. go. 3& 1st by aging 12% solutions of thepartially polymer- 3 3; 81 j 1 ized resin described in Example 2 at roomtemperature.

Appearance of 1% dilutions Mols acid after- Soln. No. Solvent used permol pH IGSln 5-6 8-10 1 hr. 1 day days days 1 Water 0.1 acetic. Notdispersible at 12% solids 2 60% aq. glycerol. ..do 5.3 ppt... col.- eolgel. .3 60% aq. glycol... .do 5 l ppt co1. 001--.. gel.

0.5 acetic. 4.5 ppt 001.... 001.... gel. 60 No acid... 7.2 mm... mm.ppt..-. ppt.

0.05HOL. 5.5 ppt. ppt.... col Col. 7 80% aq. glycerol -..do 5.4 ppt..001--.. col. clear,

The colloidal condition is reached in a considerably shorter time whenthe above solutions are aged at 70-l00 0., even when only smallquantities of acid are used. Thus, for example, a 12% resin solution ina solvent composed of 95% glycerol, 5% water and 0.01 mol acetic acidper mol of melamine showed colloidal properties upon dilution with waterto 1% resin solids after only six hours aging at 100 C.

The application of a large number of aged melamine-formaldehyde resinsolutions containing aqueous glycol, glycerol and other water-solublepolyhydroxy compounds to rayon fabrics has shown that satisfactoryretention is obtainable with only slightly polymerized resins, but thatin all cases at least a small amount of acid must be present. However,these solvents permit the reduction of the quantity of acid to the pointwhere washing of the fabric is unnecessary. Although this is anadvantage in the commercial pretreatment of fabrics it must beemphasized that the impregnating solution should not contain more than afew percent of resin, on the order of 0.5-6% or less, as otherwise thefabric will become stifiened when the resin is cured.

The following is typical of results obtainable with water-solublepolyhydroxy compounds and small amounts of acid. In all cases the resinsolution was acidified and aged at 12% resin solids, then diluted to 1%and applied to the fabric which was cured ten minutes at 200 F.Duplicate samples were impregnated, the first being dried directly andthe second being washed and dried. The quantity of acid in the followingties of cellulosic textiles which comprises the steps of impregnatingsaid textiles in a bath prepared by aging an aqueous solution of amelamineformaldehyde condensation product in a solvent comprising apolyhydric alcohol and sufllcient acid to reduce the pH to about 4.5-6.8until a colloidal melamine-formaldehyde resin solution is formed,whereby colloidal particles of the resin are deposited on the cellulosictextiles in amounts of 0.01-2% of the dry weight thereof.

4. A method of improving the bonding properties of textiles containinghighly oriented cellulose filaments which comprises impregnating saidtextiles in a bath prepared by aging an aqueous solution of amelamine-formaldehyde condensation product containing chloracetic aciduntil a colloidal melamine-formaldehyde resin solution is formed,whereby colloidal particles of the resin are deposited on the cellulosictextiles in a water-insoluble condition in amounts of 0.01- 0.5% of thedry Weight thereof.

5. A method of improving the bonding properties of textiles containinghighly oriented cellulose filaments which comprises first impregnatingsaid textiles with alcoholic alkali and organic carboxylic acid and thenimpregnating the textiles with an acidic aqueous colloidal solution ofpartially polymerized melamine-formaldehyde resin, whereby 0.015% of theresin is retained on the textiles in a water-insoluble condition.

6. .A method of improving the bonding properties of rayon textiles whichcomprises impregnating them with an acidic aqueous colloidal sotablerepresents mols of acetic acid per mol'of lution ofmelamine-formaldehyde resin in a solmelamine. vent comprising awater-soluble polyhydric alco- Aging Per cent Soln Solvent Mols g fzFabric Resin in No. Acid Temp 80m Washed Dry 0 Days Fabric 1 glycerol.0.1 140 8 1.35 1A .do 0.1 140 s 1.69 2.- 80% glyceroL 0.1 140 8 0.07 2A..do 0.1 140 s 1.59 3. 60% glycolo. 1 140 s 1. 35 3A.. do 0.1 140 6 1.454 100% glycol 0.1 140 6 0.08 4A -.do 0.1 140 s 0.73

These retention figures show clearly the importance of colloid formationon the retention of resin when the fabric is washed. When the resinsolution has aged to the colloidal, cationic condition it is adsorbed bythe textile fibers in a water-insoluble condition, whereas the resintaken up from the clear solutions was easily washed from the fabric.

What I claim is: V

1. A method of improving the bonding properties of cellulosic textileswhich comprises impregnating said textiles with an acidic aqueous holand retaining 0.01-2% of resin on the rayon in a water-insolublecondition.

7. A method of improving the bonding properties of cellulosic textileswhich comprises impregnating said textiles with an aqueous solution ofcolloidal melamine-formaldehyde resin in a solvent comprising awater-soluble polyhydric alcohol and a small amount of acid sufficientto reduce the pH to 4.5-6.8 and drying the textiles and curing thewater-insoluble resin on the fibers thereof.

JOHN D. POLLARD.

REFERENCES CITED The following references are of recordin the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,345,543 Wohnsiedler Mar. 28,1944 2,191,362 Widmer Feb. 20, 1940 2,185,477 Thompson Jan. 2, 19402,197,357 Widmer Apr. 16, 1940 2,097,589 Dreyfus Nov, 2, 1937 2,385,383Schroy Sept, 25, 1945

